This application is a 371 of PCT/JP00/02211 filed Apr. 6, 2000.
1. Field of Invention
The present invention is directed to a process for preparing spinel-type lithium manganate, and more specifically to a process for preparing spinel-type lithium manganese, from which eluting amount of manganese after prepared it into an anode material for non-aqueous electrolyte secondary battery is reduced, and which can improve performance of the battery under high temperature, such as preservation property and cycle property under high temperature.
2. Background Art
Based on recent rapid shift to miniaturized and cordless electronic hardware, such as personal computers and telephones, a need for using secondary batteries as a driving power source is becoming very intensive. Among the secondary batteries, the biggest interest is directed to non-aqueous electrolyte containing secondary battery since it can be the smallest in size and can generates high energy density. As the anode material for non-aqueous electrolyte containing secondary battery which facilitates such desires as described above, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4), etc. can be used, for example. Each of these complex oxides has a voltage more than 4 V to lithium, and therefore, a battery having high energy density can be obtained by using any of such complex oxides.
Among the complex oxides described above, LiCoO2 and LiNiO2 have a theoretical capacity of more or less 280 mAh/g, while LiMn2O4 has a smaller theoretical capacity of 148 mAh/g. However, LiMn2O4 can be suitably used for EV use because the resource of the raw material, manganese dioxides, is plenty and is cheaper in cost as well as no cause of thermal instability at charging like LiNiO2.
However, lithium manganate (LiMn2O4) has a problem of elution of Mn therefrom at a high temperature, which gives inferior battery property, such as preservation and cycle property under high temperature.
Therefore, it is an object of the present invention to provide a process for preparing spinel-type lithium manganate, which can reduce the eluting amount of manganese at charging when it is used as an anode material for non-aqueous electrolyte containing secondary battery and can improve the battery property under high temperature, such as preservation and cycle properties under high temperature, an anode material composed of the lithium manganate and a non-aqueous electrolyte containing secondary battery using the said anode material.
In solving the problem described above, the first invention of the present invention directing to a process for preparing spinel-type lithium manganate is characterized by admixing the electrolyzed manganese dioxide, which is prepared by neutralizing the manganese dioxide precipitated by means of electrolysis with any of potassium hydroxide, potassium carbonate and lithium hydroxide, and a lithium material and then subjecting the resulting mixture to a sintering process.
The second invention of the present invention is directed to the process specified in the first invention, wherein pH of the electrolyzed manganese dioxide being neutralized with either potassium hydroxide or potassium carbonate is 2 or more.
The third invention of the present invention is directed to the process specified in the first invention, wherein the electrolyzed manganese dioxide being neutralized with lithium hydroxide contains lithium in an amount of 0.02-0.5% by weight.
The fourth invention of the present invention is directed to the process specified in the first, second and third inventions described above characterized in that the manganese dioxide is pulverized either before or after the neutralization with any of potassium hydroxide, potassium carbonate and lithium hydroxide.
The fifth invention of the present invention is directed the fourth invention, wherein the average particle size of the pulverized manganese dioxide is in a range of from 5 to 30 xcexcm.
The sixth invention of the present invention is directed to the process specified in any of the first to the fifth inventions, wherein the sintering process is operated at a temperature higher than 750xc2x0 C.
The seventh invention of the present invention is directed to an anode material to be used for non-aqueous electrolyte containing secondary battery, wherein the anode material is composed of the spinel-type lithium manganate obtained according to the process specified in any of the first to the sixth inventions.
The eighth invention of the present invention is directed to a non-aqueous electrolyte containing secondary battery, wherein the secondary battery is composed of an anode using the anode material for non-aqueous electrolyte containing secondary battery specified in the seventh invention, a cathode capable of occluding and de-occluding either lithium alloy or lithium and non-aqueous electrolyte.